This invention relates to catalysts for producing phenol and processes for producing phenol from benzoic acid through vapor phase oxidation in the presence of the catalyst.
Heretofore, various catalysts and processes were developed for producing phenol from benzoic acid through catalytic oxidation in vapor phase. For example, Japanese Patent KOKAI No. 57-11932 discloses a catalyst for producing phenol composed of at least one of copper compounds, vanadium compounds, silver compounds, lithium compounds, sodium compounds and magnesium compounds, and a process for producing phenol using the above catalyst. Another catalyst and process are disclosed in Japanese Patent KOKOKU No. 59-20384. The catalyst contains oxidized copper, zirconium and alkali metal, and the process uses them supported on .alpha.-alumina carrier as the catalyst. Moreover, Japanese Patent KOKOKU No. 64-934 discloses a process for producing phenol using an oxide catalyst composed of many kinds of metal elements, i.e. molybdenum as the essential element, at least one of vanadium, niobium and tantalum, at least one of copper, silver, manganese, iron, cobalt, nickel, rhodium, palladium and platinum, and at least one of thallium, alkali metals and alkaline earth metals.
However, the catalyst disclosed in Japanese Patent KOKAI No. 57-11932 is insufficient in the yield of phenol. Actually, the maximum conversion of benzoic acid was 50.5%, and the maximum selectivity to phenol was 88.6%, and therefore, the maximum yield was 44.7%. Besides, when an exothermic reaction is conducted such as the oxidation reaction of benzoic aicd using the catalyst containing a copper compound, hot spots occur in the catalyst layer to progress calcining of the catalyst. As a result, the catalytic activity is degraded sharply. In the manufacturing process disclosed in Japanese Patent KOKOKU No. 59-20384, the yield of phenol is insufficient. That is, the maximum conversion of benzoic acid was 63.7%, and the maximum selectivity to phenol was 82.2%, and therefore, the maximum yield was 52.4%. Moreover, byproducts such as diphenyl oxide are produced abundantly, and therefore, a purification process for the produced phenol is necessary. In the manufacturing process disclosed in Japanese Patent KOKOKU No. 64-934, the maximum conversion of benzoic acid was 75%, and the maximum selectivity to phenol was 89%. Therefore, the maximum yield was 66.8%. Moreover, all of the above conventional processes are inferior in productivity due to low space time yield (the production amount of phenol per unit volume of catalyst per unit time), and therefore, they are disadvantageous in the industrial production of phenol.